1. Heat oven to 180 degrees C.
2. Mix the butter and sugar together in a large bowl.
3. Add in the eggs, mixing in each one at a time.
4. Sift in the flour, then mix in the lemon and lime zest.
5. Pour mixture into loaf tin and stick in the oven for about an hour. The top will go golden and you should be able to stick a skewer in and pull it out clean.
6. When the cake is done, mix the tbsp of sugar into the lemon juice, prick some holes into the cake and pour the mixture over.
7. Leave to cool for as long as possible.